Integrated circuit

ABSTRACT

An integrated circuit has at least two circuit components ( 1, 2 ), which are formed on a semiconductor substrate ( 13 ) of a first conductivity type and each of which has a self-contained supply voltage system; the integrated circuit has at least one coupling circuit which connects the same potentials (Vss 1 , Vss 2 ; Vcc 1 , Vcc 2 ) of the two supply voltage systems in such a way as to intercept the voltage peaks. The coupling circuit includes at least one transistor (T 1 , T 2 , T 3 ) with a base ( 20, 21, 22 ) of the first conductivity type, and a collector ( 15, 16, 17, 18 ) and emitter ( 15, 16, 17, 18 ) of a second conductivity type, the base of which transistor is connected through a resistor (R) to the potentials (Vss 1 , Vss 2 ) of the two supply voltage systems, and the collector and emitter of which are directly connected to one of these potentials.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to the field of integratedcircuits, and in particular to integrated circuits that include at leasttwo circuit components that are formed on a common semiconductorsubstrate and which each have self-contained supply voltage systems.

[0002] Integrated circuits may include at least two circuit componentsthat are formed on a common semiconductor substrate and which each haveself-contained supply voltage systems. In addition, each of the twocircuit component may include self-contained bonding spots for receivingan externally supplied voltage. Separate supply voltage systems of thistype may be necessary to meet EMC requirements. In conventionaltechnologies for highly integrated circuits, the semiconductor substrateis p-conductive and is connected to the power supply nodes of the twocircuit components that carry the lowest voltage potential “Vss” amongthe applied potentials, such that the Vss potentials of the two circuitcomponents are coupled by one substrate resistance.

[0003] One or more connections in the form of signal lines are oftenpresent between the two circuit components. The desirable isolation ofthe supply voltage systems for the individual circuit components maylead to problems in the event of excessive voltages (EOS, electricaloverstress). This is particularly true in the event of electrostaticdischarge (ESD), since the supply voltage systems of the individualcircuit components occupy a relatively smaller area and supply a smallernumber of components than does a corresponding system comprising theentire integrated circuit. Therefore, such supply voltage systems reactwith greater sensitivity to the switching operations of individualcomponents, and differential voltages are transferred from one circuitcomponent to another through the signal lines and are thus able to reachsensitive circuit components, such as the gate-oxide layers, which maybe destroyed by these voltages.

[0004] A prior art technique includes coupling the supply voltagesystems for multiple circuit components integrated on a commonsemiconductor substrate using coupling circuits, as shown in FIG. 1.FIG. 1 is a schematic illustration of a prior art integrated circuit 100that includes first and second circuit components 1, 2, respectively.The first and second circuit components 1, 2 receive supply potentialsVcc1, Vss1, or Vcc2, Vss2, as shown through bonding spots 5. Undernormal operating conditions Vccl=Vcc2, and Vss1=Vss2. The integratedcircuit 100 also includes first and second coupling circuits 3, 4. Thefirst coupling circuit 3 receives Vcc1 and Vcc2 on lines 102, 103respectively, while the second coupling circuit 4 receives Vss1 and Vss2on lines 104, 105 respectively. Each coupling circuit includesantiparallel connections of two PNP transistors 6. Whenever excessvoltage mutually disturbs the supply voltage systems of the first andsecond circuit components 1, 2, the transistors 6 produce a compensationof voltage, such that a portion of the current flows from the emitter tothe base, while the rest continues to flow to the collector.

[0005] The PNP transistors 6 each have the semiconductor substrate asthe collector, an n-doped well formed in the substrate as the base, anda p⁺ region inside the well as the emitter. The effect of thisarrangement is that when one of the coupling circuits 3, 4 opens inresponse to an excessive voltage of one of the transistors 6, althoughpart of the compensation current (from the emitter to the base) willflow from one supply voltage system into the other, another partnevertheless will unavoidably flow directly from the emitter into thesubstrate representing the collector.

[0006] A problem with these conventional coupling circuits is theconsiderable area they utilize on the substrate. Considerable area isrequired because each of the coupling circuits, one of which is requiredfor each supply voltage to be compensated, has two transistors 6. Anaddition considerable area is required is because essentially holes areinvolved in the current flow through the transistors 6. The mobility ofholes is less than that of electrons, and therefore requirecomparatively greater coverage areas of the doping zones in order toachieve a volume resistivity of the transistors that is sufficiently lowfor effective coupling.

[0007] Therefore, there is a need for an integrated circuit thatincludes at least two circuit components and separate supply voltagesystems for the different circuit components, which integrated circuithas coupling circuit that has a small surface area requirement betweenthe supply voltage systems.

SUMMARY OF THE INVENTION

[0008] A base of the transistor is preferably formed by the substrateitself, or, more precisely, by a region of the substrate contiguous withcollector doping zones and emitter doping zones of the transistor, andthe resistance between the base and the potentials of the two systemscoupled by the coupling circuit is the intrinsic resistance of thesubstrate between its region forming the base and one of each contactdoping zone that is conductively connected to the collector or emitterthrough a metallization applied to the substrate. To obtain an identicalcoupling behavior for the transistor in both directions, the collectorand emitter of the transistor are preferably symmetrical, such that thearrangement may also be termed a transistor with a double emitter.

[0009] The coupling circuit may be implemented with a single transistor,the dimensions of which are fixed by the desired volume resistivity.Greater flexibility of design with respect to accommodating the couplingcircuit on one substrate surface without an increased area requirementis provided by employing multiple transistors. These may as a rule bedistributed independently of each other on the substrate surface.

[0010] A space-saving design results by creating the transistors using aplurality of doping zones of the second conductivity type, which arealternately connected to the first or second of the two power supplypotentials. Specifically, if a doping zone connected to the power supplypotential of the first circuit component is surrounded on both sides—ineach case with an intermediate base zone having the natural doping ofthe substrate—by doping zones connected to the power supply potential ofthe second circuit component, then the resulting arrangement is theequivalent of two parallel transistors. In an arrangement of this type,the surface area requirement for two transistors is significantly lessthan the double-sized space requirement needed for two individualtransistors. This savings in space may be increased even further if morethan two transistors are created by providing an alternating arrangementof doping zones connected to the two power supply potentials.

[0011] To ensure the same behavior of these transistors, the transistordoping zones should be appropriately arranged in series in anequidistant configuration. The contact doping zones are preferablylocated at the ends of the series. In one embodiment two contact dopingzones are sufficient for a plurality of transistors.

[0012] In the case of this type of series arrangement of contact dopingzones and emitter-forming doping zones, preferably each emitter-formingdoping zone directly adjacent to a contact doping zone is metallicallyconductively connected to this contact doping zone. In the event of anexcess voltage, this arrangement reduces the risk of a breakdown betweena contact doping zone connected to the first circuit component and aemitter-forming doping zone connected to the second circuit component.

[0013] To achieve identical coupling behavior in both directions, thenumber of emitter-forming doping zones of the second conductivity typeis an even number for the symmetry for the coupling circuit. In oneembodiment the number of doping zones may be four—which corresponds to aparallel circuit of three transistors.

[0014] To avoid the undesirable interaction between the transistors ofthe coupling circuit and the circuit components, at least one transistorof the coupling circuit may be surrounded by a shielding doping zone ofthe second conductivity type. A shielding doping zone of this type isbiased in the nonconducting direction, such that a barrier layer isformed between this zone and the substrate.

[0015] The shielding doping zone preferably runs in an annular patternalong the surface of the substrate. It thus does not prevent everycurrent flow from the at least one transistor of the coupling circuitthrough the substrate to the circuit component, but rather forces thecharge carrier to follow an alternate route into the depth of thesubstrate. This increases the route length, and thus the effectiveresistance of the substrate, between the transistors of the couplingcircuit and the circuit components. The contact doping zones of thecoupling circuit are preferably surrounded by the shielding doping zone.

[0016] These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of preferred embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

[0017]FIG. 1 is a schematic illustration of a prior art integratedcircuit;

[0018]FIG. 2 is a schematic illustration of a coupling circuit;

[0019]FIG. 3 is a plot of the current-voltage characteristic of thecoupling circuit illustrated in FIG. 2;

[0020]FIG. 4 shows an example having the surface structure of a couplingcircuit according to an aspect present invention;

[0021]FIG. 5 is an equivalent circuit diagram of the surface structurein FIG. 4;

[0022]FIG. 6 shows a modification of the surface structure of FIG. 4;

[0023]FIG. 7 shows a further modification of the surface structure inFIG. 6;

[0024]FIG. 8 is a cross-section through the structure of FIG. 7 of thesurface structure in FIG. 6;

[0025]FIG. 9 shows a further modification of the surface structure.

DETAILED DESCRIPTION OF THE INVENTION

[0026]FIG. 2 is a schematic illustration of a coupling circuit 200,which may be utilized as a replacement to the coupling circuitillustrated in FIG. 1. The coupling circuit 200 includes an NPNtransistor 11, the geometry and doping of which are symmetrical. Thetransistor 11 includes a first emitter 202 that is connected on a line204 to first voltage potential Vss1, and a second emitter 206 that isconnected on a line 208 to second voltage potential Vss2. The two powersupply potentials Vss1, Vss2 are each connected through identicalresistances 12 to transistor base 210.

[0027]FIG. 3 is a plot 300 of the current-voltage characteristic of thecoupling circuit illustrated in FIG. 2. Current is plotted alongvertical axis 302 and voltage is plotted along horizontal axis 304. Inresponse to small differences between the two power supply potentials,the behavior is resistive and is determined by the resistances 12 (FIG.2). The activity of the transistor 11 is activated in response toincreasing voltages, and the compensating current 1 flowing through thecoupling circuit 200 increases with voltage V at a greater than linearrate.

[0028]FIG. 4 illustrates a first example of a coupling circuit 400. Thecoupling circuit 400 includes a plurality of doping zones 14-19 formedadjacently in a series on a p-doped semiconductor substrate. The mostexternal of these zones are p⁺-doped and designated as the contactdoping zones 14, 19. The intermediate zones, that is the emitter dopingzones 15-18, are n⁺-doped. Surface metallizations of the doping zones14, 16, 18 are connected to first voltage potential Vss1, while those ofthe doping zones 15, 17, 19 are connected to the second voltagepotential Vss2. Surface strips 20, 21, 22 of substrate 13 are locatedbetween the emitter doping zones 15-18, and have the original p-dopingof the substrate in a doping concentration unaltered by the generationof doping zones 14-19. The surface strips 20, 21, or 22 each function asthe base of a symmetrical transistor, the two emitters of which areformed by the two emitter doping zones contiguous with the relevantsurface strips 20. In the event of a voltage difference between Vss1 andVss2, the contact doping zones 14, 19 allow a flow of current throughthe substrate 13 from one contact doping zone 14, 19 to another. Thiscurrent flow determines the corresponding electrical potentialseffective in the region of individual surface strips 20-22. Theequivalent circuit diagram shown in FIG. 5 thus corresponds to thelayout of FIG. 4. The two middle emitter doping zones 16, 17 of thelayout of FIG. 4 correspond to the two symmetrical npn transistors T1,T2, or T2, T3, the bases of which are each formed by surface strips 20,21, 22. The resistances R between contact doping zone 14, the bases ofthe transistors, and contact doping zone 19 result from the lowintrinsic conductivity of the weakly doped substrate 13.

[0029]FIG. 6 shows another design for a layout of a coupling circuit.The design differs from the layout of FIG. 4 in that the emitter zonesconnected to Vss1 or Vss2 are transposed such that the respectiveadjacent doping zones 14 and 15, or 18 and 19, are connected in parallelthrough a metallization. The fact that this approach increases thedistance, compared to the layout of FIG. 4, between the contactimplantation zones 14 or 19 and the immediately adjacent emitter dopingzones 16, 17 connected to the other power supply voltage-thereby alsoincreasing the substrate resistance by a corresponding amount-reducesthe risk that an excess voltage pulse will cause a breakdown at the pnboundary of the emitter doping zones. That is, the dielectric strengthis enhanced, as compared with the layout of FIG. 4, with the samedimensioning and arrangement of the doping zones; or the width of thesurface strips between contact doping zones 14, 19 and adjacent emitterdoping zones 15 or 18 may be reduced with the dielectric strengthremaining the same, thereby further decreasing the space requirement ofthe coupling circuit.

[0030]FIG. 7 shows a further modification of the layout design of FIG.6. Since the transistors formed by surface strips 20-22 and the adjacentemitter doping zones 15-18 are connected to substrate 13, a shieldingdoping zone 23 is provided to reduce the interactions between thetransistors of the coupling circuit and the elements of circuitcomponents 1, 2. The shielding doping zone is formed by n-doping with ahigh penetration depth into the substrate 13. On the surface of thesubstrate 13, the shielding doping zone 23 is highly n-doped on a smallcross-sectional area so as to form a contact zone 25, which is inconductive contact with a metallization 24 deposited on the substratesurface. The shielding doping zone has low n-doping over the majority ofits cross-section, as indicated by the widely spaced hatching, and alower doping concentration than in the other n-doped emitter dopingzones. As the cross-section in FIG. 8 shows, the shielding doping zone23 significantly lengthens the current path from the emitter dopingzones 15-18 to the adjacent elements of the circuit components 1 or 2(not shown in FIG. 7). The effect of the shielding is due here to apositive potential applied to the shielding doping zone 23 over themetallization area 24, which potential results in the formation of abarrier layer at the pn junction between the shielding doping zone 23and the substrate 13.

[0031]FIG. 9 shows another modified design for the layout of FIG. 6. Theshielding doping zone 23 is configured in an annular shape whichsurrounds emitter doping zone 15-18. In contrast to the design of FIG.7, the contact zone 25 is not arranged in an annular configurationaround the transistors of the coupling circuit but is limited to twoislands, each of which is conductively connected to one of the twopotentials Vss1, Vss2.

[0032] Since it is possible to keep the doping concentration low inshielding doping zone 23, its conductivity may be maintained at a lowvalue similar to that of the substrate 13.

[0033] Although the present invention has been shown and described withrespect to several preferred embodiments thereof, various changes,omissions and additions to the form and detail thereof, may be madetherein, without departing from the spirit and scope of the invention.

What is claimed is:
 1. Integrated circuit including at least two circuitcomponents (1, 2), which are formed on a semiconductor substrate (13) ofthe first conductivity type and which each have a self-contained supplyvoltage system, and including at least one coupling circuit whichconnects the same potentials (Vss1, Vss2; Vccl, Vcc2) of the two supplyvoltage systems so as to intercept voltage spikes, characterized in thatthe coupling circuit includes at least one transistor (T1, T2, T3) witha base (20, 21, 22) of the first conductivity type, and a collector (15,16, 17, 18) and emitter (15, 16, 17, 18) of a second conductivity type,the base of which is connected through a resistance (R) to thepotentials (Vss1, Vss2) of the two supply voltage systems, and thecollector and emitter of which are connected directly to one of thesepotentials.
 2. The integrated circuit of claim 1, wherein the base (20,21, 22) of the transistor (T1, T2, T3) is a region of the substrate(13), and that the resistance (R) is the intrinsic resistance of thesubstrate (13) between the base (20, 21, 22) and a contact doping zone(14, 19) metallically connected to the collector or emitter.
 3. Theintegrated circuit of claim 2, wherein the collector and emitter of thetransistor are symmetrical.
 4. The integrated circuit of claim 3,wherein the coupling circuit includes a plurality of transistors (Ti,T2, T3) connected in parallel between the power supply potentials (Vss1,Vss2).
 5. The integrated circuit of claim 4, wherein the transistorscomprise a plurality of doping zones (15, 16, 17, 18) of the secondconductivity type, which doping zones are alternately connected to thefirst (Vss1) or the second (Vss2) of the two power supply potentials. 6.The integrated circuit of claim 5, wherein the doping zones (15, 16, 17,18) are arranged in an equidistant configuration.
 7. The integratedcircuit of claim 6, wherein the doping zones (15, 16, 17, 18) of thesecond conductivity type are extended transversely relative to theseries.
 8. The integrated circuit of claim 7, wherein the contact dopingzones (14, 19) are located at the ends of the series.
 9. The integratedcircuit of claim 8, wherein each contact doping zone (14, 19) in theseries is adjacent to a doping zone (15, 18) of the second conductivitytype which is metallically connected to the zone.
 10. The integratedcircuit of claim 9, wherein the number of doping zones (15,. 16, 17, 18)of the second conductivity type is an even number.
 11. The integratedcircuit of claim 10, wherein the circuit has four doping zones (15, 16,17, 18) of the second conductivity type.
 12. The integrated circuit ofclaim 11, wherein the at least one transistor is surrounded by ashielding doping zone (23) of the second conductivity type.
 13. Theintegrated circuit of claim 12, wherein the shielding doping zone (23)is biased in the nonconducting direction.
 14. The integrated circuit ofclaim 12, the shielding doping zone (23) extends in an annularconfiguration along the surface of the substrate (13).
 15. Theintegrated circuit of claim 14, wherein a highly doped contact zone (25)is formed in the shielding doping zone (23).
 16. The integrated circuitof claim 15, wherein the contact zone (25) includes two islands, each ofwhich is conductively connected to one of the potentials (Vss1, Vss2) ofthe two supply voltage systems.
 17. The integrated circuit of claim 15,wherein the contact doping zones (14, 19) are formed on the shieldingdoping zone (23).